Rigidochromism of tetranuclear Cu(i)–pyrazolate macrocycles: steric crowding with trifluoromethyl groups

Abstract

Macrocyclic Cu(I)–pyrazolate tetramers (Cu₄pz₄) can fold into compact structures with luminescent Cu₄ cores whose emission wavelengths are sensitive to steric effects along the periphery of the macrocycle. Introducing CF₃ at the C4 position of 3,5-di-^tBu-pyrazolate increases steric crowding that modifies the conformational behavior of the Cu₄pz₄ complex, highlighted by a low-temperature martensitic transition. Variable-temperature analysis of solid-state luminescence reveal an unexpected blueshifting of emission with rising temperature.